Lithography



United States Patent 6 LITHGGRAPHY Elbert A. Dulfer, Burlingame, Calif.

No Drawing. Application May 20, 1953 Serial No. 356,303

2 Claims. (Cl. 101-1493.)

In my prior patent application, Serial No. 251,809, filed October 17, 1951 now abandoned, of which this is a continuation-in-part, I disclosed that certain water insoluble soaps could advantageously be employed in the process of making deep-etched lithographic plates. I have now found that by employing certain metal salts in a non-aqueous solution, that even superior results can be obtained to the process heretofore disclosed. Therefore,

this invention relates to an improved process of makinglithographic plates employing certain metallic salts, as hereinafter defined.

In the conventional process of making a deep-etched lithographic plate, a grained metal plate such as aluminum or zinc is coated with a film of a light hardenable substance such as a dichromated colloid, and the coated film is exposed to a high intensity light through a positive transparency of the desired subject matter. In the light colored areas of the positive image, that is, those areas where it is desired that the finished plate not print, the gelatin is hardened while in the areas which are dark colored in the positive and which correspond to printing surfaces, the gelatin is protected from the light and is unhardened. The plate is developed by means wellknown to those skilled in the art. Typical developing agents include an acidulated aqueous solution of a salt such as calcium chloride, magnesium chloride, zinc chloride, or iron perchloride, or an acid such as lactic acid, acetic acid, phosphoric acid or the like. This develop ment or etching renders the areas which are to print receptive to the greasy printing ink.

However, in the conventional process for preparing lithographic plates, it is necessary that the plate be very thoroughly wiped with anhydrous alcohol prior to the application of the ink, since the ink does not tend to selectively displace the etching solution. This anhydrous alcohol wash is one of the most troublesome steps in the process of preparing a lithographic plate and if it is not properly done, the whole plate may be ruined. It is the alcohol washing step which requires most skill and care in the preparation of a plate, and the elimination of this step would be a great advance in the art.

Although others have proposed various processes by which the alcohol wash can be eliminated, the proposed processes have made no impression on the ,prior art.

It is an object of my invention to provide a process in which a lithographic plate is made by an inexpensive and rapid process and which does not require great skill or care in the preparation of the plate.

It is a further object of this invention to provide a plate which does not require the use of anhydrous alcohol in its preparation.

Another object of this invention is to provide a plate which has long wearing qualities and which gives press runs on the order of hundreds of thousands of copies.

Still another object of this invention is to provide a plate which may be repaired while it is on the press. By repaired, I refer to the process hereinafter outlined wherein the plate can be treated while it is on the press if the plate shows signs of losing its ink retentive properties during the course of a run.

Still another object of my invention is the provision of a process whereby a lithographic plate is made and the bare metal is not exposed to the atmosphere or any oxidizing condition, at any time during manufacture. By elimination of any possible oxidation of the plate, high ink retention and long wearing qualities are obtained.

Another object of this invention is to provide a process wherein a metal is deposited on printing areas of the plate in an ink retentive form.

Still another object is to provide a lithographic plate with a low lint pick up, permitting the use of low grade paper in the lithographic process.

In general, the objects of my invention are accomplished by following the conventional deep-etch solution which is used in the preparation of lithographic plate-s, by a treatment with a hydrophobic, oily substance which tends to selectively wet the metal plate and to displace any aqueous solution therefrom. The oily substance is applied directly to the plate which is still wet from the etching step without any intermediate treatment.

I have found that the objects of the present invention can be accomplished by employing a wide variety of metal salts dissolved in, or dispersed in, a non-aqueous solvent such as acetone or alcohol. A particularly advantageous solvent is about equal parts of alcohol and 2- butoxyethanol.

It has been found that the metals which may be employed do not necessarily bear any particular relationship in the electromotive series to the metals from which the plate is made. However, I have found it advantageous to employ a metal salt in which the metal is different than the metal from which the plate is made. Although this invention is not predicated on any theory of its operation, I believe that the metal salts are decomposed in situ, forming crystalline masses on the plate of extremely high ink receptive properties. In normal lithographic plates, there is a tendency for dots to become lost as the ink is squeezed from the dots, allowing the enroachment of the fountain solution, which tends to emulsify and thus dislodge the dot. However, the dots on plates made in accordance with the present invention have extremely high ink retaining properties and resist this action. It is believed that the unusually high ink retentive properties are due to the formation of the crystylline mass on the plate.

The preferred metals for use in conjunction with the present invention are lead, chromium, copper, nickel and aluminum, although other metals such as iron, tin, silver, arsenic, magnesium, manganese, and the like can be used. Similarly, I prefer to use the nitrates and/or chlorides, although other metal salts such as the oxides or stearates, can be used. It is frequently advantageous to combine two or more of the metal salts. Thus, particularly good results have been obtained with mixtures of nickel chloride and cuprous chloride; mixtures of chromium chloride with nickel chloride; and mixtures of aluminum stearate with nickel chloride. The following non-limiting examples are certain preferred compositions of my treating agent.

Example I /2 gallon 2-butoxyethanol /2 gallon methanol 1 /2 pounds nickel chloride /2 pound cuprous chloride Example II /2 gallon Z-butoxyethanol A gallon methanol /2 pound lead nitrate /2 pound chromium chloride 1 pound nickel chloride V 3 Example III /2 gallon 2-butoxyethano1 /2 gallon methanol /2 pound aluminum stearate 1 pound nickel chloride Normally, I employ the metal salts up to about the limit of solubility in the particular solvent chosen, and ordinarily prefer to use from about 10% to 25% of the metal salt in solution.

By the use of an agent in the solution which selectively oil wets the metal plate, it is possible to entirely eliminate the use of anhydrous alcohol in the preparation of the plate. Much less care is necessary in making plates by this improved method and it may be done by a relatively unskilled worker. Further, since the plate is not exposed to oxidation by the air at any time, a better bond is made between the ink receptive film and the metal surface. This contributes greatly to the long life of plates made by this process.

In making long runs with conventional plates, it frequently happens that the bond is lost between the ink receptive film and the metal. When this happens, certain spots on the plate go blind and no longer pick up ink. With conventional plates there is no remedy for this problem and it is necessary to start from the beginning and prepare an entirely new plate. However, with a plate made in accordance with my improved process, it has been found that if the plate tends to go blind, it is not even necessary to remove the plate from the press to repair it. It is only necessary to apply the solution of one of the Water soluble salts mentioned above to the plate While it is on the press and then reapply ink. It will be found that the plate is no longer blind and can be used for thousands more copies.

The following examples illustrate a preferred method of carrying out my process.

A lithographic plate was prepared according to the normal procedure, well-known to those skilled in the art, through the deep-etch stage. As soon as the plate had been deep-etched, and while it was still wet with the deepetch solution, the plate was treated with a saturated solution made up in accordance with Example I, above. The solution was washed onto the plate and the plate kept wet with the solution for a period of about five minutes. After such treatment, the plate was treated in the conventional manner, i. e., it was then coated with developing ink, the developing ink was removed from the nonprinting areas, and the plate was run on a press. A plate made in this manner is capable of reproducing an image having a screen of 300 lines per inch.

It Will be noted that in the above example, the solution of metal salt was applied to the plate immediately after the plate had been deep-etched and While the plate was still wet. This is in direct contrast with the prior art processes wherein the plate is carefully washed after the deep-etch stage. In my process, it is not only unnecessary to wash the plate, but actually undesirable. For instance, if in preparing a plate one washes the plate in the conventional manner with alcohol, and then attempts to apply a solution of metal salts, it is found that the plate does not accept ink and that the plate has been ruined so far as carrying out the present invention is concerned.

It has been found that when using such a plate, there is less pick-up of lint from the printing paper which is transferred from the blanket to the plate and thus into the ink supply. Ordinarly, the pick-up from lint from the paper is a limitation in the lithographic process and prevents one from using the lower grades of paper. However, with plates prepared according to my process, the lithographic process can be used quite satisfactorily on cheap grades of paper such as ordinary newsprint stock.

The water insoluble salt solutions of the present invention may be made with any of the well-known solvents for such salts. Acetone is preferred as the solvent because of its low cost and efiectiveness, but other solvents such as hydrocarbon fractions, alcohol, ethers, cellulose esters and the like may be used. It is sometimes desirable to incorporate with the water insoluble salt a bodying agent which will tend to make the salt solution more viscous, but such bodying agents have not been found to be necessary. Suitable bodying agents included nitrocellulose, ethylcellulose, hydroxyethylcellulose and the like.

- I claim:

1. As a new composition of matter, a material for treating a lithographic plate comprising one-half gallon Z-butoxyethanol, one-half gallon methanol, 1 /2 pounds nickel chloride, one-half pound cuprous chloride.

2. As a new composition of matter suitable for treating a lithographic plate, a composition comprising onehalf gallon 2-butoxyethanol, one-half gallon methanol, one-half pound aluminum stearate, one pound nickel chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,956 Misuraca Oct. 14, 1941 2,297,929 Wise Oct. 6, 1942 2,342,713 Wescott Feb. 29, 1944 2,390,944 King Dec. 11, 1945 2,429,107 Peters et a1 Oct. 14, 1947 2,437,005 Schwarz Mar. 2, 1948 FOREIGN PATENTS 547,795 Great Britain Sept. 11, 1942 OTHER REFERENCES Clerc: Ilford Manual of Process Work, 4th edition, 1946, Ilford, Ltd., London, page 242.

Soderstrom: The Lithographers Manual 1940, Waltwins Pub. Co., N. Y., page 240. 

1. AS A NEW COMPOSITION OF MATTER, A MATERIAL FOR TREATING A LITHOGRAPHIC PLATE COMPRISING ONE-HALF GALLON 2-BUTOXYETHANOL, ONE-HALF GALLON METHANOL, 1 1/2 POUNDS NICKEL CHLORIDE, ONE-HALF POUND CUPROUS CHLORIDE. 